The subject of the present invention is a power feed apparatus for milling machines, which when the power is engaged feeds material to be milled more evenly than is possible by hand and in which the power is disengaged automatically at the end of a cut, thereby obviating the necessity for constant supervision by the machine operator.
The conventional milling machine includes a stand, and a quill housing on the stand, containing a motor for a rotary cutting tool which projects downward toward a table. The table moves horizontally on the stand, by means of a feed screw, which engages the table and the stand. The feed screw is rotated by a hand crank handle at either end. Alternatively, the feed screw can be rotated by a power feed which incorporates a motor and replaces one of the crank handles. This has the advantage that the table and the material mounted on it for milling are moved under the cutting tool at a uniform rate, producing a smoother cut. The other crank handle remains available for manual operation of the feed screw.
Various power-feed devices, such as that disclosed in U.S. Pat. No. 3,490,335 (King) are available for attachment to milling machines, but most are either large and cumbersome or require manual disengagement at the end of every cut. For example, the King patent, supra, discloses power feed means having a motor, a motor output gear, a feed screw gear and an idler gear. The idler gear is movable by a lever or crank from a first position out of engagement with either of the other gears to a second position in engagement with both the motor output gear and the feed screw drive gear. It is retained in the latter position by an interlock through which the lever passes.
Milling machines are conventionally equipped with adjustable stops which, when screwed down tightly in a slot in the edge of a milling table, prevent the table from moving any farther under the influence of its feed screw and thereby stop a cut at the desired length. When the table reaches its stops, the feed screw is unable to rotate. If the feed screw is being driven by a power feed like that in the King patent, supra, when the feed screw and its drive gear stop rotating, so do the idler gear and the motor output gear which are in engagement with the drive gear. Since power is still being applied to the motor while its shaft is stopped, the motor will overheat and be damaged and/or blow its fuse unless the gears are manually disengaged. Thus, constant supervision by the machine operator is necessary.
Accordingly, it is a primary object of this invention to equip a power feed with means for automatically disengaging the motor gear from the feed screw drive gear whenever during the milling operation the table stop or any predetermined level of resistance is encountered.
It is a further object of this invention to provide a power feed which will feed at a constant rate and disengage itself repeatedly after exactly the same length of cut.
It is a further object of this invention to provide a power feed which will reverse direction with the flip of a toggle switch.
It is a further object of this invention to provide such an apparatus which is lightweight, which can be installed quickly and which does not interfere with manual operation.